Ngozi Okonjo-Iweala's nomination is the first time that a non-US candidate has been a serious challenger for the top job at the World Bank. Photograph: Yuri Gripas/Reuters

The World Bank presidency will not be decided on merit, candidate Ngozi Okonjo-Iweala told reporters Monday as the institution prepared to make its appointment.

The World Bank is poised to announce its new president today – choosing between Nigerian finance minister Okonjo-Iweala and frontrunner Jim Yong Kim, president of Dartmouth College and the US's nomination.

The World Bank presidency has gone to a US candidate since the organisation was founded at the Bretton Woods conference at the close of the second world war.

This is the first time that a non-US candidate has been a serious challenger for the job. But on Monday Okonjo-Iweala said: "You know this thing is not really being decided on merit."

"It is voting with political weight and shares, and therefore the United States will get it," she told reporters at a briefing on the country's 2012 budget.

A third candidate, Colombia's former finance minister Jose Antonio Ocampo, pulled out of the race Friday, calling the selection process a "political-oriented exercise".

Okonjo-Iweala said that although she expected her challenge to the US's nomination to fail, the process "will never ever be the same again".

"So we have won a big victory. Who gets to run the World Bank – we have shown we can contest this thing and Africa can produce people capable of running the entire architecture," she said.

Kim, a physician by training, was a surprise nomination for the role. The 52-year-old is a leading figure in global health and a former director of the HIV/Aids department at the World Health Organization. He was born in Seoul, South Korea, and moved with his family to the US at the age of five.

The US dominates the voting for the World Bank and can usually rely on European countries to back its candidate. The International Monetary Fund has been headed by a European since its creation in 1944, and the latest managing director, France's Christine Lagarde, was appointed with US support.